Yes, at that time, the idea of South Slavic unity was very strong.
Among Serbs, biggest proponents were socialists Svetozar Markovic and Dimitrije Tucovic, politicians Ilija Garasanin, Milovan Milovanovic and historian Milos S. Milojevic and many others. Among Bulgarians, Vasil Levski, Lyuben Karavelov, Miladinov brothers etc.
Question of Macedonia remain greatest stumbling stone between Serbian and Bulgarian nationalists.